Ada County, Idaho: drinking water report. Ada County – Boise and surrounding communities – serves about 530,000 residents.
Ada County – Boise and surrounding communities – serves about 530,000 residents. The City of Boise draws from the Boise River and from deep groundwater wells. United Water (now Veolia) operates the Boise water system, which benefits from a combination of mountain-fed surface water and a clean aquifer. The Treasure Valley's rapid population growth has put increasing pressure on both supply and infrastructure.
Boise's water quality is among the best of any mid-sized US city. The Boise River originates in the central Idaho mountains, and the local aquifer is deep and well-protected. UCMR5 data shows minimal PFAS detections in the Boise system – the county does not host major military installations or heavy industrial PFAS sources.
The primary concern in Ada County is growth-related. According to the Idaho Department of Environmental Quality's 2024 monitoring data, all Ada County public water systems met federal contaminant limits. But the Treasure Valley's population has grown by over 40% since 2010, and water infrastructure is being built and expanded rapidly to keep pace.
Ada County residents are in a relatively strong position on water quality. The main risk is complacency – as growth continues, source water protection and treatment capacity need to keep pace.
Check your water for current data in your area. Even with a clean supply, a basic carbon filter can improve chlorine taste. Our water filter guide covers options for different needs. Pull your detailed report, and visit our Idaho page for statewide context.
Drinking water is one exposure route. These federal datasets also cover Ada County, ID.
The EPA places Ada County, ID in Zone 2 - a moderate-risk category, with a predicted average indoor radon level between 2 and 4 pCi/L. Zone maps predict an area's radon potential from geology and existing indoor readings; they say nothing about a specific house. Testing is the only way to know your own level.
29% of homes in Ada County, ID were built before 1980, and 6% before 1950. Residential lead paint was banned in 1978, so housing age is the strongest available proxy for lead-paint exposure. This describes the county's housing stock, not any one home.
Modelled annual fine-particle pollution (PM2.5) in Ada County, ID averages 9 µg/m³, within the EPA's annual standard of 9 µg/m³. These are CDC modelled county estimates rather than readings from a specific monitor.
How radon zones work · Air quality by county · Lead exposure guide
Across 64 public water systems serving Ada County, ID with EPA lead testing on record, 3 (4.7%) reported a 90th-percentile lead result above the EPA's 15 ppb action level, and the median is 3 ppb. 24 water systems serving Ada County, ID carry a health-based EPA Safe Drinking Water Act violation.
| Most-cited violation type | Systems affected |
|---|---|
| Ground Water Rule | 12 |
| Revised Total Coliform Rule | 6 |
| Combined Uranium | 4 |
| Total Coliform Rule | 3 |
| Lead and Copper Rule | 3 |
Source: EPA Lead and Copper Rule 90th-percentile tap sampling and EPA SDWIS Safe Drinking Water Act enforcement records, aggregated from the public water systems serving this county. Figures are counts of water systems, not a test of any individual home or tap.